You cannot use the Online version to file a 2019 return. The Online version is only to prepare the current year's tax return (now is for 2020). You can use the Online version for your 2020 return.
To file your return with TurboTax you will need to purchase the Desktop version of TurboTax which you install on your computer. You will need to mail in your 2019 return. You can purchase the 2019 tax software from TurboTax at the following website.
https://turbotax.intuit.com/personal-taxes/past-years-products/